Sync based timing recovery schemes generally assume no multipath characteristics for the received signal. When operating over a channel exhibiting long multipath profiles (significant temporal dispersion or significant delay spread), such timing recovery schemes can break down because correlation peaks may become indistinct (that is, either clear correlation peaks are not apparent or false peaks manifest). In effect, the long channel impulse response smears any underlying correlation peaks, making precise peak detection impossible.
Temporal dispersion in the received signal due to multipath interference is generally corrected by an equalizer in the receiver. A simplistic solution to the problem of multipath interference with correlation peaks would be to rectify the temporal dispersion utilizing an equalizer; however, a conventional receiver structure requires both carrier and timing recovery to be operative before equalization may be effectively employed.
The problem is thus circular in nature, with successful equalization requiring timing recovery to be operative and ideal sync based timing recovery for a multipath signal requiring equalization to be operative. In short, using a full equalizer to clean up the sync correlation peaks is neither advisable nor feasible.
There is, therefore, a need in the art for improvement of timing recovery despite multipath interference.